|Convair B-58 of the United States Air Force|
|Role||Supersonic strategic bomber|
|National origin||United States|
|First flight||11 November 1956|
|Introduction||15 March 1960|
|Retired||31 January 1970|
|Primary user||United States Air Force|
|Developed into||Convair Model 58-9|
The B-58 was developed during the 1950s for the United States Air Force (USAF) Strategic Air Command (SAC). To achieve the high speeds desired, Convair adapted the delta wing used by contemporary fighters such as the Convair F-102. The bomber was powered by four General Electric J79 engines in underwing pods. It had no bomb bay: it carried a single nuclear weapon plus fuel in a combination bomb/fuel pod underneath the fuselage. Later, four external hardpoints were added, enabling it to carry up to five weapons.
The B-58 entered service in March 1960, and flew for a decade with two SAC bomb wings: the 43rd Bombardment Wing and the 305th Bombardment Wing. It was considered difficult to fly, imposing a high workload upon its three-man crews. Designed to replace the subsonic Boeing B-47 Stratojet strategic bomber, the B-58 became notorious for its sonic boom heard on the ground by the public as it passed overhead in supersonic flight.
The B-58 was designed to fly at high altitudes and supersonic speeds to avoid Soviet interceptors. But with the Soviet introduction of high-altitude surface-to-air missiles, the B-58 was forced to adopt a low-level-penetration role that severely limited its range and strategic value. It was never used to deliver conventional bombs. The B-58 was substantially more expensive to operate than other bombers, such as the Boeing B-52 Stratofortress, and required more frequent aerial refueling. The B-58 also suffered from a high rate of accidental losses. These factors resulted in a relatively brief operational career of ten years. The B-58 was succeeded in its role by the smaller, swing-wing FB-111A.
The genesis of the B-58 was the Generalized Bomber Study (GEBO II) issued in February 1949 by the Air Research and Development Command (ARDC) at Wright-Patterson AFB, Ohio, for the development of a supersonic, long-range, manned bomber aircraft. ARDC sought the best attainable quantitative data, challenging the industry to devise their own solutions to attain the stated goal. Work on the proposed bomber's design was to begin less than two years after sustained supersonic flight had been achieved. According to aviation authors Bill Gunston and Peter Gilchrist, while some military officials were keenly interested in the prospective use of supersonic bombers, others held doubts about the propulsion systems and materials science required for supersonic operations, as well as the much higher fuel consumption relative to subsonic counterparts.
Despite the scepticism, multiple contractors submitted bids for GEBO II, which was viewed as an influential step towards a development contract. These included Boeing, Convair, Curtiss, Douglas, Martin and North American Aviation. The majority of submissions were relatively straightforward, unambitious, and expensive. Convair, which had built the XF-92A and other delta-wing fighters, evaluated swept and semi-delta configurations, then settled on the delta wing, which offered good internal volume for support systems and fuel. It also provided low wing loading for the airframe size, permitting supersonic flight in the mid-stratosphere at 50,000 to 70,000 ft (15,000 to 21,000 m). Most of the configurations studied mated the delta wing to a relatively slender fuselage housing a crew of two and powered by a pair of jet engines.
The Convair proposal, coded FZP-110, was a radical two-place delta wing bomber powered by three General Electric J53 turbojet engines. The performance estimates included a 1,000 mph (1,600 km/h) speed and a 3,000-mile (4,800 km) range. A key feature of the design was to store consumables, both weaponry and most of the fuel, within a large external pod, which enabled a smaller fuselage. In January 1951, Convair submitted the FZP-110 proposal, which was received later than other competing bids. During December 1951, a revised FZP-016 proposal was submitted, which deleted the third engine on the tail, increased the remaining two engines' thrust, and added a third crew member to operate defensive systems.
The Air Force chose Boeing's MX-1712 and Convair MX-1626 design studies to proceed to a Phase 1 study. During this period Convair took advantage of recent developments by General Electric and replaced the two large J53 engines with four smaller J79s optimized for supersonic flight. The recently formulated area rule was also applied to the design, resulting in aerodynamic re-profiling and an even more slender fuselage. Having been refined, Convair redesignated their renewed submission MX-1964.
In August 1952, Convair's design was judged superior. According to Gunston and Gilchrist, Boeing's submission was viewed as equally good, but their separate contract to produce the Boeing B-52 Stratofortress had undoubtedly influenced this competition. In December 1952, Convair was chosen to meet the new SAB-51 (Supersonic Aircraft Bomber) and SAR-51 (Supersonic Aircraft Reconnaissance) standards, the first General Operational Requirements (GOR) for supersonic bombers. In February 1953, the Air Force issued a contract for Convair's design, designated B-58 on 10 December 1952.
The B-58 program, unlike those for preceding military aircraft, is now recognised as the first weapon system contract. Under this arrangement, Convair acted as the prime contractor responsible for all program elements, not just the aircraft. Convair was required to devise or subcontract everything associated with the aircraft's operation, from the engines to training manuals, spare components, and software, in excess of one million items. Early on, the contract was modified to build a pair of XB-58 prototypes, 11 YB-58A pre-production aircraft, and 31 mission pods including a free-fall bomb pod, a rocket-propelled controllable bomb pod, a reconnaissance pod, and an electronic reconnaissance pod.
The first prototype, serial number 55-660, was rolled out on 31 August 1956. The program was performed under high security: prior to the roll out, no unauthorized individual had knowledge of its shape or basic configuration. On 11 November 1956, the maiden flight occurred. The prototype exceeded Mach 1 for the first time on 30 December of that year. The difficult and protracted flight test program involving 30 aircraft continued until April 1959. A total of 116 B-58s were produced: 30 trial aircraft and 86 production B-58A models. Most of the trial aircraft were later upgraded to operational standards. Eight were equipped as TB-58A training aircraft.
Convair sought further development of the B-58, proposing variants and derivatives for both military and civil applications. Most would never go beyond the drawing board, having been ordered prior to the decision to terminate multiple contracts. The B-58B, B-58C, B-58D, and B-58E variants were all terminated prior to completion of any production aircraft. During the late 1960s, some refinements to the existing fleet were developed and introduced, such as slender bomb racks (known as Multiple Weapons Capability) and additional pods. The final B-58 was delivered in October 1962.
The Convair B-58 Hustler was a high speed strategic bomber, capable of attaining routinely Mach 2 at altitude. It incorporated a large delta wing with a leading-edge sweep of 60° and was powered by an arrangement of four General Electric J79-GE-1 turbojet engines. Although its sizable wing generated relatively low wing loading, it proved to be surprisingly well suited for low-altitude, high-speed flight. To protect against the heat generated while cruising at Mach 2, the crew compartment, the wheel wells and electronics bay were pressurized and air conditioned. The B-58 was one of the first extensive applications of aluminum honeycomb panels, which bonded outer and inner aluminum skins to a honeycomb of aluminum or fiberglass.
Various features of the B-58 were considered to be record-breaking, according to Gunston and Gilchrist. The structure itself made up 13.8 per cent of the aircraft's gross weight, an exceptionally low figure for the era, while the wing was considered to be extremely thin as well. Several key features of the engine, including the nacelle and the inlet, were unlike any existing aircraft, having been devised from guidance by aerodynamicists. Specifically, the inlets used moving conical spikes, being fully aft on the ground and at low speeds to maximise air intake, then driven forward while being flown at high speeds to minimise the annular gap. This movement was automatically controlled, but significant noise and asymmetric thrust would be generated in the event of a single inlet malfunctioning.
The B-58 was operated by a crew of three: pilot, bombardier/navigator, and defensive systems operator. They were seated in separated tandem cockpits. The pilot's cockpit, which was provided with very deep windows, was considered to be mostly conventional for a large multi-engine aircraft. The defensive systems operator was provisioned with a complex arrangement of different systems, which Gunston and Gilchrist describe as being the most complicated of any aircraft of the era. The space allocated to the crew, despite being roughly half of the fuselage's internal volume, was typically considered to be cramped and claustrophobic.
Later versions of the B-58 provided each crew member with a novel ejection capsule that could eject at an altitude of 70,000 ft (21,000 m) at speeds up to Mach 2. Unlike standard ejection seats of the period, a protective clamshell would enclose the seat and the control stick with an attached oxygen cylinder, allowing the pilot to continue to fly even "turtled up" and ready for immediate egress. The capsule was buoyant; the crewmember could open the clamshell, and use it as a life raft. Unusually, the ejection system was tested with live bears and chimpanzees; it was qualified for use during 1963. The XB-70 would use a similar system with capsules of a different design.[circular reference]
The electronic controls were ambitious and advanced for the day. The navigator and DSO's cockpits featured wraparound dashboards with warning lights and buttons, and automatic voice messages and warnings from a tape system were audible through the helmet sets. Research during the era of all-male combat aircraft assignments revealed that a woman's voice was more likely to gain the attention of young men in distracting situations. Nortronics Division of Northrop Corporation selected actress and singer Joan Elms to record the automated voice warnings. To those flying the B-58, the voice was known as "Sexy Sally". The original voice recordings are archived.
While the B-58's performance and design were exceptional for the era, it was not an easy aircraft to fly. This was caused by the 60° leading edge sweepback of its wing and was inherent in these types of delta wing platforms. It required a much higher angle of attack than a conventional aircraft, up to 9.4° at Mach 0.5 at low altitudes. If the angle of attack was too high, in excess of 17°, the bomber could pitch up and enter a spin. Several factors could prevent a successful recovery: if the pilot applied elevon, if the center of gravity was not correctly positioned, or if the spin occurred below 15,000 feet (4,600 metres), recovery might not be possible. The B-58 also possessed unconventional stall characteristics; if the nose was elevated, the bomber maintained forward motion without pitching down. Unless large amounts of power were applied, the descent rate increased rapidly. Another problem pilots faced was called "fuel stacking", taking place whenever the B-58 accelerated or decelerated. It was caused by fuel movement within the tanks, which led to sudden changes in the aircraft's center of gravity. This could cause the B-58 to abruptly pitch or bank, potentially resulting in a loss of control.
The aircraft had unusual takeoff requirements, with a 14° angle of attack needed for the rotation at about 203.5 knots (376.9 km/h; 234.2 mph) for a 150,000-pound (68,000 kg) combat weight. This poor takeoff performance was evident with the high landing speed, necessitating a drogue parachute for braking, which was also required for B-47 and B-52 aircraft. To accommodate the high landing speed, the specially configured landing gear had to handle excessive conditions, both the inflation pressure and wheel rpm were far greater than prior units in order to cope.
The Sperry AN/ASQ-42 bombing/navigation system combined a sophisticated inertial navigation system with the KS-39 Star tracker (astro-inertial navigation system) to provide heading reference, the AN/APN-113 Doppler radar to provide ground speed and windspeed data, a search radar to provide range data for bomb release and trajectory, and a radar altimeter. The AN/ASQ-42 was estimated to be 10 times more accurate than any previous bombing/navigation system.
Defensive armament consisted of a single 20 mm (0.79 in) T-171E-3 rotary cannon with 1,200 rounds of ammunition in a radar-aimed tail barbette. It was remotely controlled through the Emerson MD-7 automated radar fire-control system only requiring the DSO to lock-on a selected target blip on his scope and then fire the gun. The system computed aiming, velocity or heading differential, and range compensation. Offensive armament typically consisted of a single nuclear weapon, along with fuel tanks, in a streamlined MB-1C pod under the fuselage. Incurable difficulties with fuel leakage resulted in the replacement of the MB-1C with the TCP (Two Component Pod), which placed the nuclear weapon in an upper section while the lower fuel component could be independently jettisoned. This had the added benefit of allowing the pilot to "clean up" the aircraft for fuel efficiency or in case of emergency, while still retaining the (somewhat) slimmer weapon.
From 1961 to 1963, the B-58 was retrofitted with two tandem stub pylons under each wing root, adjacent to the centreline pod, for B43 or B61 nuclear weapons for a total of five nuclear weapons per aircraft. Although the USAF looked at using the B-58 for conventional strikes, it was never equipped for carrying or dropping conventional bombs. A photo reconnaissance pod, the LA-331, was also fielded. Several other specialized pods for ECM or an early cruise missile were considered, but not adopted. The late-1950s High Virgo air-launched ballistic missile was designed to be launched from the B-58; a Hustler carried out four test launches to determine ballistic missile and anti-satellite weapon system capability.
On 1 August 1960, the B-58 was declared operational, nine months after the delivery of the first aircraft to the Air Force. One month later, a single B-58 participated in the annual SAC Combat Competition at Bergstrom; it proved itself to be superior to competing Boeing B-47 Stratojets and Boeing B-52 Stratofortresses, securing first place in both high-level and low-level radar bombing exercises.
Crews were typically chosen from other strategic bomber squadrons. Due to some characteristics of delta-winged aircraft, new pilots used the Convair F-102 Delta Dagger as a conversion trainer, before moving to the TB-58A trainer. The B-58 was found to be difficult to fly and its three-man crews were constantly busy, but its performance was exceptional. A lightly loaded Hustler would climb at nearly 46,000 ft/min (235 m/s). In addition to its much smaller weapons load and more limited range than the B-52, the B-58 had been extremely expensive to acquire.
Through FY 1961, the total cost of the B-58 program was $3 billion ($21 billion in 2019 dollars). A highly complex aircraft, it also required considerable maintenance, much of which required specialized equipment and ground personnel. For comparison, the average maintenance cost per flying hour for the B-47 was $361, for the B-52 it was $1,025 and for the B-58 it was $1,440. The B-58 cost three times as much to operate as the B-52. The cost of maintaining and operating the two operational B-58 wings (39 aircraft per wing) equaled that of six wings of B-52s (only 15 aircraft per wing). Because of the support costs of six wings vs only two wings, the actual cost per aircraft of the B-52s were $1.42 million per year vs $1.21 million per year for the B-58 (this figure included special detailed maintenance for the nose landing gear, which retracted in a complex fashion to avoid the center payload).
Compounding these exorbitant costs, the B-58 had a high accident rate: 26 B-58 aircraft were lost in accidents, or 22.4% of total production; more than half of the losses occurred during flight tests. The SAC senior leadership had been doubtful about the aircraft type from the beginning, although its crews eventually became enthusiastic about the aircraft. General Curtis LeMay was never satisfied with the bomber, and after a flight in one declared that it was too small, far too expensive to maintain in combat readiness and required an excessive number of aerial refuelings to complete a mission. Although the high altitude ferry range of the B-58 was better than that of the B-47s, the lack of forward basing resulted in a requirement for more KC-135 tanker support.
Two SAC bomb wings operated the B-58 during its operational service: the 43rd Bombardment Wing (which later transitioned to the 43rd Airlift Wing), based at Carswell AFB, Texas from 1960 to 1964, and Little Rock AFB, Arkansas from 1964 to 1970; and the 305th Bombardment Wing, based at Bunker Hill AFB (later Grissom AFB), Indiana from 1961 to 1970. The 305th also operated the B-58 combat crew training school (CCTS), the predecessor of the USAF's current formal training units (FTUs).
By the time the early problems had largely been resolved and SAC interest in the bomber had solidified, Secretary of Defense Robert McNamara decided that the B-58 was not a viable weapon system. It was during the B-58's introduction that high-altitude Soviet surface-to-air missiles (SAM) became a threat, especially the SA-2 Guideline, a SAM system the Soviet Union extensively deployed. The "solution" to this problem was to fly at low altitudes, minimizing the radar line-of-sight and reducing exposure time.
Because of dense air at low altitudes, the B-58 could not fly at supersonic speeds and its moderate range was reduced further, negating the costly high-speed performance of the aircraft. Despite shortcomings, the type had its advocates within the service; according to Gunston and Gilchrist, when Secretary McNamara had requested proposals for a new manned Mach 2 bomber, General Thomas S. Power responded with a request for the B-58 to be put back into production. In late 1965, McNamara ordered retirement of the B-58 by 1970; the principal reason given for this directive was the high sustainment cost for the fleet. On 29 October 1969, the Department of Defense announced that the type would be withdrawn from service on 31 January 1970.
Despite efforts of some officials within the Air Force to secure a reprieve, the phaseout proceeded on schedule. The last B-58s were retired in January 1970, after which they were placed into storage with the Military Aircraft Storage and Disposition Center (MASDC) at Davis-Monthan Air Force Base. The fleet survived intact until 1977, at which point nearly all remaining aircraft were sold to Southwestern Alloys for disposal. As a weapons system, the B-58 was replaced by the FB-111A. This aircraft was designed for low-altitude attack, to be more flexible with the carriage of conventional weapons, and less expensive to produce and maintain.
Since B-58 pilots were the only USAF pilots experienced in long-duration supersonic flight, several former Hustler crew members were selected by Colonel Douglas Nelson to fly the Lockheed SR-71 Blackbird at the start of that program.
A number of B-58s were used for special trials. One was specially modified to test the Hughes radar system intended for the Lockheed YF-12 interceptor and the North American F-108 Rapier, which had an extended nose to accommodate the radar and was nicknamed "Snoopy" (see Aircraft on Display). Several improved (and usually enlarged) variants, named B-58B and B-58C by the manufacturer, were proposed but never built.
The B-58 set 19 world speed records, including coast-to-coast records, and the longest supersonic flight in history. In 1963, it flew from Tokyo to London (via Alaska), a distance of 8,028 miles (12,920 km), with 5 aerial refuelings in 8 hours, 35 minutes, 20.4 seconds, averaging 938 miles per hour (1,510 kilometres per hour). As of 2016[update], this record still stands. The aircraft was serving in an operational unit, and had not been modified in any way besides being washed and waxed. One of the goals of the flight was to push the limit of its new honeycomb construction technique. The speed of the flight was limited only by the speed at which they believed the honeycomb panels would delaminate, although one of the afterburners malfunctioned and the last hour of the flight was continued at subsonic speed. This reduced the average speed to roughly Mach 1.5, despite most of the flight being at Mach 2. This B-58 was called "Greased Lightning" – the codename for the record attempt.
On 3 June 1961 B-58A 59-2451 Firefly crashed during the Paris Air Show, killing all three on board. The aircraft had earlier made the first supersonic transatlantic crossing between New York and Paris in less than 3 hours 20 minutes.
In September 1961, a B-58 on training flight from Carswell Air Force Base suffered a fire and failure of the left main gear. A chase aircraft was sent to examine the aircraft in flight. Through the night, eight sessions of aerial refuellings were conducted, using an improved technique, and once daylight broke a successful emergency landing was made at Edwards Air Force Base. The Air Force made a training film about the incident, including film of the landing.
On December 8, 1964, a B-58 carrying nuclear weapons slid off an icy runway on Bunker Hill Air Force Base in Bunker Hill, Indiana and caught fire during a training drill. The five nuclear weapons on board were burned, including one 9-megaton thermonuclear weapon, causing radioactive contamination of the crash area.
On 15 June 1965, at the Paris Air Show, Lt. Colonel Charles D. Tubbs was killed and two other crewmen injured when their B-58 crashed. The aircraft landed short of the runway, struck the instrument approach beacons and burst into flames.
Data from Quest for Performance
Jimmy Stewart, a bomber pilot during World War II and a brigadier general in the Air Force Reserve, appeared in the Air Force documentary film B-58 Champion of Champions. In the film, Stewart flew in the back seat of the B-58 on a typical low-altitude attack.
In the film Fail Safe, the attack on Moscow is made by a squadron of "Vindicator" bombers, fictitious aircraft. While exterior shots of the plane relied on footage of B-58s, interior shots depicted a three-man crew, similar to that of a conventional airliner, and distinct from the tandem seating on a real B-58. The fictional Vindicator bomber was again represented by the B-58 in Fail Safe, a 2000 made-for-TV remake starring George Clooney.
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